Method for photographically producing electrical conductor patterns inside a hollow object



March 5, 1963 Filed Nov. 29. 1957 METHOD FOR PHOTOGRAPHICALLY PRODUCING GLASS TUBE R W. GILBODY ET AL.

ELECTRICAL CONDUCTOR PATTERNS INSIDE A HOLLOW OBJECT Fig. I

2 Sheets-Sheet l CLEAN WITH TRICHLOROETHYLENE POUR IN PHOTO RESIST TO COAT TUBE INTERIOR SURROUND TUBE WITH PHOTOGRAPHIC NEGATIVE 8| EXPOSE REMOVE UNEXPOSED RESIST WITH TRICHLOROETHYLENE COAT IMAGE WITH COLLOIDAL SUSPENSION OF GRAPHITE IN WATER FIRE 375C FOR 5 MINUTES COOL WASH TUBE OUT WITH WARM WATER Roger W. GiIbody Clifford R. WoIker INVENTORS March 5, 1963 R. W. GILBODY ETAL METHOD FOR PHOTOGRAPHICALLY PRODUCING ELECTRICAL CONDUCTOR PATTERNS INSIDE A HOLLOW OBJECT Filed Nov. 29. 1957 2 Sheets-Sheet 2 Roger W. Gilbody Clifford R. Walker INVENTORS printed electrodes and conducive leads are connected to the electrodes and pass United States PaterrtO METHOD FOR PHOTOGRAPHICALLY PRODUC- ING ELECTRICAL CONDUCTGR PATTERNS IN- SIDE A HOLLOW OBJECT Roger W. Gilbody, Nashua, N.H., and Cliiiord R. Walker, Dracut, Mass., assignors to Sanders Associates, Inc, Nashua, N.H., a corporation of Delaware Filed Nov. 29, 1957, Ser. No. 699,796 6 Claims. (Cl. 96-35) This invention relates to an article of manufacture and improved method of marking or printing on surfaces transparent to radiant energy and more particularly to miniature photo-conductor tubes and a method of printing electrodes on the interior surface thereof.

One type of prior art photo-conductor tubes has electrodes which are manually applied to the inside surface of the tube envelope with a brush. A disadvantage of such an arrangement is that the resulting tubes must be at least large enough to lend themselves readily to the maneuvering of a brush Within the cell blank or unsealed tube. A further disadvantage of such a method is that it makes uniformity and mass production of such tubes quite dilficult. While the present invention is subject to a wide range of applications, it is especially suited for use in printing circuits inside small diameter transparent tubes and will be particularly described in that connection.

It is an object of this invention, therefore, to provide an improved method of printing circuits on transparent surfaces.

Another object of this invention is to provide a simple and inexpensive method of producing a pattern of any desired configuration on a surface transparent to radiant energy which does not lend itself readily to the manual application of said pattern.

A further object of this invention is to provide a method of printing electrodes on the inside surface of photo-conductor tubes, to enable unlimited miniaturization of such tubes.

In accordance with the invention, there is provided a method of marking in a desired pattern a surface of an object having an area transparent to radiant energy. The method comprises coating the surface with a compound sensitive to radiant energy and exposing the compound coating to radiant energy passing through the transparent area to produce a latent image of a desired configuration on the compound coating. The undesired or excess compound coating is removed to leave the desired marking pattern.

In accordance with the invention there is further provided, as an article of manufacture, a miniature photoconductor tube. The tube comprises an envelope transparent to radiant energy and has electrodes printed on its inside surface by means of a radiant energy sensitive compoundexposed to an image projected through the transparent tube envelope. A lead sulphide coating covers the the area therebetween. A pair of through the tube envelope for transmitting the energy from the electrodes to a circuit.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is a flow chart illustrating the process of printing a conductive pattern on the inside surface of a glass tube in accordance with the invention; FIG. 2 is a perspective view partly in section of a glass ice tube illustrating the exposure of a coating of the inside surface to radiant energy.

FIG. 3 is a side elevation view of a sealed photo-conductor cell having electrodes printed therein in accordance with the principles of the invention.

FIG. 4 is a side elevation view of an unsealed cell blank similar to that of FIG. 3, but rotated and FIG. 5 is a side elevation view of the cell blank of FIG. 3 rotated through an angle of Referring now to the drawings and with particular reference to FIGS. 1 and 2, there is here illustrated the process for depositing or printing a conductive pattern on the inside surface of a glass tube 11. The process is described in steps as follows:

(1) Cleaning the glass tube 11 with tri-chloroethylene 12 and permitting the tri-chloroethylene to evaporate until the tube is dry.

(2) Pouring in a photo-resist 13, such as the cinnamic acid ester of polyvinyl alcoho1,'and thoroughly coating the tube interior with the resist.

(3) Pouring out any excess resist 13, and permitting the resist to dry. p I

(4) Surrounding glass tube 11, with a photographic negative 19, as shown in FIG. 2.

(5) Exposing the resist through the negative to an appropriate light source 14.

(6) Removing any unexposed resist with tri-chloroethylene to evaporate 15.

(7) Coating the image with the colloidal suspension of graphite in water, such as Aquadag made by the Acheson Colloids Corporation of Port Huron, Michigan, 16. (The colloidal graphite may be incorporated in the photo-resist at the outset to eliminate this step in the process. This is not necessarily advantageous, however, as the black pigment absorbs so much light that it acts as a light filter and prevents exposure of the photo-resist.)

(8) Firing at 375 C. for five minutes followed 'by gradual cooling to prevent breakage of the glass 17.

(9) Washing out glass tube 11 with warm water 18. Considering now the process just described and referring to FIGS. 3, 4 and 5, there is here illustrated a photo-conductor tube embodying the teaching of this invention. The cell blank 23 is preferably formed from a glass tube having an outside diameter of, for example 0.390 inch, and an inside diameter, for example, of 0.360 "inch. A pair of leads 24 and 25, formed, for example from nickel 0.020 of an inch in diameter, are then fused to the tube. The ends of leads 24 and 25 extending into the tube are curved to follow the tube contour as shown, and silver pasted in place. The leads '24 and 25, protruding outside the cell blank 23, are cut to an appropriate length,'as for example 1 /2 inches. Electrodes 26 and 27 shown cross-hatched are then printed inside cell blank-23 as described above. The photo-resist 13' for coating the inner surface of cell blank 23 is introduced through the open end 28, exposed to light 14 and developed in-ac cordance with the above described process. The electrode composition resulting from this process possesses good conductivity characteristics and exhibits a bond strength between the carbon and the glass which is far superior to bondstrengths achieved by manual application of the colloidal graphite. The electrodes 26 and 27 are subsequently coated, for example with a lead sulphide or other light sensitive film, covering the area 29 encompassed by the dotted line in FIGURES 3, 4 and 5.

While applicant does not intend to be limited to any particular tube shapes or sizes in the embodiment of the invention just described, there follows a set of overall dimensions which have been found to be particularly suitable for a miniature photo-conductor tube. '1

inch. & inch.

portion of cell blank 23 inch. Width of flattened sealed bottom portion A2 inch.

These tolerances are readily maintained by printing of the electrodes in the manner just described. The relative position of photographic negative 19, tube 11, photoresist coating 13, and light source 14 are illustrated in the exploded view of FIGURE 2. It should be noted, however, that to obtain uniform results negative 19 should, during exposure, be in physical contact with the outside of tube 11 just as resist coating 13 is in contact with the inner surface of tube 11.

It is apparent from the above considerations that a carbon configuration of the type described could be electroplated or a metallic suspension, as for example colloidal silver, gold, or copper, could be used with a photo resist instead of carbon. Likewise, any number of varieties of radiant energy sources could be used in combination with an appropriate photo resist. For example, materials can be used as photo resists that will polymerize when exposed to radiant energy such as ultraviolet light, gamma radiation, microwave energy and X- rays. Radiant energy of these types can be focused into desired pattern by using a material impervious to the energy type but apertured in the appropriate configuration.

A further use for the process of this invention lies in the fact that opaque configurations may be accurately deposited in places where they are resistant to wear. An example of this would be the printing of a thermometer scale on the inside surface of the thermometer tube. Other examples are the printing of numerals on the inside surface of tiny watch crystals, printing scales on scientific instruments and printing reticle's.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: k

1. A method of providing electrical conductors in a desired conductive pattern on the inside surface of a hollow object having an area transparent to a radiant energy source which comprises: coating said surface with a photo-resist sensitive to radiant energy; disposing a model image between said radiant energy source and said transparent area; exposing said photo-resist coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desired configuration on said photo-resist coating; removing the unexposed photo-resist coating to leave said surface marked in said desired pattern; coating said pattern with a colloidal suspension of graphite; baking said object until said graphite particles adhering to said photo-resist coating are fixed; and washing ofi any unadhering graphite particles.

2. A method of providing electrical conductors in a desired conductive pattern on the inside surface of a hollow object having an area transparent to a radiant-energy source which comprises: coating said surface with a photo-resist sensitive to radiant energy; disposing a model image between said radiant energy source and said transparent area; exposing said photo-resist coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desired configuration on said photo-resist coating; removing the unexposed photo-resist coating to leave said surface marked in said desired pattern; coating said pattern with a colloidal suspension of graphite; baking said object until said graphite particles adhering to said photo-resist coating are fixed; washing off any unadhering graphite particles; and plating said conductive pattern with a metal.

3. A method of providing electrical conductors in a desired conductive pattern on the inside surface of a hollow object having an area transparent to a radiant energy source which comprises: coating said surface with a compound sensitive to radiant energy which comprises substantially fully esterified cinnamic acid ester of polyvinyl alcohol; disposing a model image between said radiant energy source and said transparent area; exposing said compound coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desired configuration on said compound coating; removing the unexposed compound coating to leave said surface marked in said desired pattern; coating said pattern with a colloidal suspension of graphite; baking said object until said graphite particles adhering to said compound coating are fixed; and washing off any unadhering graphite particles.

4. A method of providing electrical conductors in a desired conductive pattern on the inside surface of a hols low object having an area transparent to a radiant energy source which comprises: coating said surface with a compound sensitive to radiant energy which comprises substantially fully esterified cinnamic acid ester of polyvinyl alcohol; disposing a model image between said radiant energy source and said transparent area; exposing said compound coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desired configuration on said compound coating; removing the unexposed compound coating to leave said surface marked in said desired pattern; coating said pattern with a colloidal suspension of graphite; baking said object until said graphite particles adhering to said compound coating are fixed; washing ofi any unadhering graphite particles; and plating said conductive pattern with a metal.

5. A method of providing electrical conductors in a desired conductive pattern on the interior surface of a hollow cylindrical tube having an area transparent to a radiant energy source and substantially small inside diameter which comprises: coating said surface with a compound sensitive to radiant energy which comprises 'substantially fully esterified cinnamic acid ester of polyvinyl alcohol; disposing a model image between said radiant energy source and said transparent area; exposing said compound coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desired configuration on said compound coating; removing the unexposed compound coating to leave said surface marked in said pattern; coating said pattern with a colloidal suspension of graphite; baking said object until said graphite particles adhering to said compound coating are fixed; and washing off any unadhering particles.

6. A method of providing electrical conductors in a desired conductive pattern on the interior surface of a hollow cylindrical tube having an area transparent to a radiant energy source and substantially small inside diameter which comprises: coating said surface with a compound sensitive to radiant energy which comprises substantially fully esterified cinnamic acid ester of polyvinyl alcohol; disposing a model image between said radiant energy source and said transparent area; exposing said compound coating to said radiant energy passed through said model image and said transparent area to produce a latent image in a desiredconfiguration on said compound coating; removing the unexposed compound coating to leave said surface marked in said pattern; coating said pattern with a colloid-a1 suspension of graphite; baking References Cited in the file of this patent UNITED STATES PATENTS 2,491,386 Miller et a1 Dec. 13, 1949 2,493,745 Blodgett et a1 June 10, 1950 2,585,700 Strickman Feb. 12, 1952 2,600,343 Tuttle June 10, 1952 6 Minsk et a1 Feb. 23, 1954 Minsk et a1 Feb. 23, 1954 Bonning July 13, 1954 Campbell Ian. 31, 1956 Elenbass et va-l. Mar. 20, 1956 Smith et a1. May 29, 1956 OTHER REFERENCES Woodbury et a1.: Photographic Amusements, 1931, 10 American Photographic Pub. Co., Boston, Massachusetts.

pages 106-108. 

1. A METHOD OF PROVIDING ELECTRICAL CONDUCTORS IN A DESIRED CONDUCTIVE PATTERN ON THE INSIDE SURFACE OF A HOLLOW OBJECT HAVING AN AREA TRANSPARENT TO A RADIANT ENERGY SOURCE WHICH COMPRISES: COATING SAID SURFACE WITH A PHOTO-RESIST SENSITIVE TO RADIANT ENERGY; DISPOSING A MODEL IMAGE BETWEEN SAID RADIANT ENERGY SOURCE AND SAID TRANSPARENT AREA; EXPOSING SAID PHOTO-RESIST COATING TO SAID RADIANT ENERGY PASSED THROUGH SAID MODEL IMAGE AND SAID TRANSPARENT AREA TO PRODUCE A LATENT IMAGE IN A DESIRED CONFIGURATION ON SAID PHOTO-RESIST COATING; REMOVING THE UNEXPOSED PHOTO-RESIST COATING TO LEAVE SAID SURFACE MARKED IN SAID DESIRED PATTERN; COATING SAID PATTERN WITH A COLLOIDAL SUSPENSION OF GRAPHITE; BAKING SAID OBJECT UNTIL SAID GRAPHITE PARTICLES ADHERING TO SAID PHOTO-RESIST COATING ARE FIXED; AND WASHING OFF ANY UNADHERING GRAPHITE PARTICLES. 